Transform-based image coding method and device therefor

Abstract

An image decoding method according to the present document comprises the steps of: receiving residual information from a bitstream; deriving transform coefficients for a current block by performing inverse quantization on the basis of the residual information; and deriving modified transform coefficients by applying LFNST to the transform coefficients, wherein the inverse quantization is performed on the basis of a predetermined scaling list, and wherein whether to apply the scaling list can be derived on the basis of whether the LFNST is applied and a tree type of the current block.

1 . An image decoding method performed by a decoding apparatus, the method comprising:
 receiving residual information from a bitstream;   deriving transform coefficients for a current block by performing dequantization based on the residual information; and   deriving modified transform coefficients by applying an LFNST to the transform coefficients,   wherein the dequantization is performed based on a predetermined scaling list, and   wherein whether to apply the scaling list is derived based on whether the LFNST is applied and a tree type of the current block.   
     
     
         2 . The image decoding method of  claim 1 , wherein when the tree type of the current block is a single tree and the current block is a luma component, the scaling list is not applied, and
 wherein when the tree type of the current block is the single tree and the current block is a chroma component, the scaling list is applied.   
     
     
         3 . The image decoding method of  claim 2 , wherein flag information indicating whether the scaling list is available when the LFNST is performed is further received. 
     
     
         4 . The image decoding method of  claim 3 , wherein when the flag information indicates that the scaling list is not available and the LFNST has an index greater than 0, the scaling list is not applied to the luma component. 
     
     
         5 . The image decoding method of  claim 3 , wherein when the flag information indicates that the scaling list is not available and the LFNST has an index greater than 0, if the tree type of the current block is a dual-tree chroma, the scaling list is not applied to the chroma component. 
     
     
         6 . The image decoding method of  claim 3 , wherein when the flag information indicates that the scaling list is not available and the LFNST has an index greater than 0, if the tree type of the current block is a dual-tree luma, the scaling list is not applied to the luma component. 
     
     
         7 . The image decoding method of  claim 1 , wherein the current block comprises a transform block. 
     
     
         8 . An image encoding method performed by an image encoding apparatus, the method comprising:
 deriving prediction samples for a current block;   deriving residual samples for the current block based on the prediction samples;   deriving transform coefficients for the current block based on a primary transform of the residual samples;   deriving modified transform coefficients from the transform coefficients by applying an LFNST; and   quantizing the transform coefficients or the modified transform coefficients,   wherein the quantizing is performed based on a predetermined scaling list, and   wherein whether to apply the scaling list is derived based on whether the LFNST is applied and a tree type of the current block.   
     
     
         9 . The image encoding method of  claim 8 , wherein when the tree type of the current block is a single tree and the current block is a luma component, the scaling list is not applied, and
 wherein when the tree type of the current block is the single tree and the current block is a chroma component, the scaling list is applied.   
     
     
         10 . The image encoding method of  claim 9 , wherein the LFNST is not performed on the chroma component of the current block. 
     
     
         11 . The image encoding method of  claim 8 , wherein when the tree type of the current block is a dual-tree chroma and the LFNST is performed on the current block, the scaling list is not applied to the chroma component. 
     
     
         12 . The image encoding method of  claim 8 , wherein when the tree type of the current block is a dual-tree luma and the LFNST is performed on the current block, the scaling list is not applied to the luma component. 
     
     
         13 . The image encoding method of  claim 8 , further comprising:
 encoding and outputting flag information indicating whether the scaling list is available when the LFNST is performed.   
     
     
         14 . The image encoding method of  claim 8 , wherein the current block comprises a transform block. 
     
     
         15 . A non-transitory computer-readable digital storage medium that stores a bitstream generated by a method, the method comprising:
 deriving prediction samples for a current block;   deriving residual samples for the current block based on the prediction samples;   deriving transform coefficients for the current block based on a primary transform of the residual samples;   deriving modified transform coefficients from the transform coefficients by applying an LFNST;   quantizing the transform coefficients or the modified transform coefficients; and   encoding residual information related to the quantized transform coefficients to generate the bitstream,   wherein the quantizing is performed based on a predetermined scaling list, and   wherein whether to apply the scaling list is derived based on whether the LFNST is applied and a tree type of the current block.   
     
     
         16 . A method for transmitting data for image information comprising:
 obtaining a bitstream for the image, wherein the bitstream is generated based on deriving prediction samples for a current block;   deriving residual samples for the current block based on the prediction samples;   deriving transform coefficients for the current block based on a primary transform of the residual samples;   deriving modified transform coefficients from the transform coefficients by applying an LFNST;   quantizing the transform coefficients or the modified transform coefficients; and   encoding residual information related to the quantized transform coefficients to generate the bitstream, and   transmitting the data comprising the bitstream,   wherein the quantizing is performed based on a predetermined scaling list, and   wherein whether to apply the scaling list is derived based on whether the LFNST is applied and a tree type of the current block.